The Waste Isolation Pilot Plant (WIPP) in Carlsbad, New Mexico is now shut down, awaiting a $500 million recovery plan that could take years. WIPP is made of up salt caverns, which are supposed to safety entomb barrels of radioactive waste for thousands of years. The barrels contain gloves, equipment, and other waste products contaminated by nuclear weapons research, and they're often packed with kitty litter to absorb extra liquids before being sealed, hopefully for eons.

Waste Drum 68660, the one that burst, was packed at Los Alamos National Laboratory (LANL), the Manhattan Project site that is 300 miles north in New Mexico. According to the New Mexican, the LANL and its contractors made a number of missteps, including using an organic wheat-based kitty litter instead of a clay-base inorganic kitty litter. Thanks to that switcheroo, the drum ultimately contained the ingredients of a bomb. On February, the drum blasted open. Temperatures rose to 1600°F (871°) in WIPP's underground cavern, and 20 workers were exposed to low levels of radiation.

Officials tell the New Mexican the exact conditions of the explosion have not been recreated in a lab. But the organic kitty litter has been under suspicion because it can release heat as it decomposes. Waste Drum 68660 also contained nitrate salts, trace metals from a glove, and acid neutraliser to deal with its high acidity, which altogether provided the other components needed for an explosion.

LANL has never explained why it switched to organic kitty litter, though emails obtained by the New Mexicansuggest it originated with a typo in a LANL policy manual that had gone unnoticed by higher ups for over a year:

The revision, approved by LANL, took effect Aug. 1, 2012....explicitly directed waste packagers at the lab to "ENSURE an organic absorbent (kitty litter) is added to the waste" when packaging drums of nitrate salt.

Freeman went on to echo some of the possible reasons for the change bandied about in earlier emails, such as the off-putting dust or perfumed scents characteristic of clay litter. But his colleague, Mark Pearcy, a member of the team that reviews waste to ensure it is acceptable to be stored at WIPP, offered a surprising explanation.

"General consensus is that the 'organic' designation was a typo that wasn't caught," he wrote, implying that the directions should have called for inorganic litter.

Since September 2012, in fact, the LANL packed up to 5,565 barrels of radioactive waste with organic kitty litter but mis-labelled it as inorganic kitty litter—16 of these barrels are also highly acidic and contain nitrate salts like the one that burst. It took an explosion before anyone noticed the mistake.

In addition to being horrifying on its own, the February explosion raises serious question about the safety of nuclear waste storage, especially when you consider how "comically simplistic," to use the New Mexican's words, the explosion's origins seems to be. There are many more worrying details in the New Mexican story, including how LANL took other shortcuts in packing the drum and failed to inform WIPP. It certainly doesn't inspire confidence in our nation's handling of radioactive waste.